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At least 19 recordsLinked to original sources
PubMed1998

Isolation and contraction of the stress fiber.

Stress fibers were isolated from cultured human foreskin fibroblasts and bovine endothelial cells, and their contraction was demonstrated in vitro. Cells in culture dishes were first treated with a low-ionic-strength extraction solution and then further extracted using detergents. With gentle washes by pipetting, the nucleus and the apical part of cells were removed. The material on the culture dish was scraped, and the freed material was forced through a hypodermic needle and fractionated by sucrose gradient centrifugation. Isolated, free-floating stress fibers stained brightly with fluorescently labeled phalloidin. When stained with anti-alpha-actinin or anti-myosin, isolated stress fibers showed banded staining patterns. By electron microscopy, they consisted of bundles of microfilaments, and electron-dense areas were associated with them in a semiperiodic manner. By negative staining, isolated stress fibers often exhibited gentle twisting of microfilament bundles. Focal adhesion-associated proteins were also detected in the isolated stress fiber by both immunocytochemical and biochemical means. In the presence of Mg-ATP, isolated stress fibers shortened, on the average, to 23% of the initial length. The maximum velocity of shortening was several micrometers per second. Polystyrene beads on shortening isolated stress fibers rotated, indicating spiral contraction of stress fibers. Myosin regulatory light chain phosphorylation was detected in contracting stress fibers, and a myosin light chain kinase inhibitor, KT5926, inhibited isolated stress fiber contraction. Our study demonstrates that stress fibers can be isolated with no apparent loss of morphological features and that they are truly contractile organelle.

Actin Cytoskeleton↗
PubMed1985

Aortic endothelial cell during regeneration. Remodeling of cell junctions, stress fibers, and stress fiber-membrane attachment domains.

We have studied in regenerating endothelium of rat thoracic aortas (a) organization of tight and gap junctions by means of morphometry using freeze-fracture electron microscopy, (b) development of cytoplasmic actin microfilament bundles (stress fibers) by means of morphometry using thin section electron microscopy, and (c) distribution of filipin-sterol complexes in the endothelial plasma membrane using thin section and freeze-fracture electron microscopy. The index of complexity for tight junctions and the index expressing the average width of gap junctions were significantly higher in regenerating endothelium than in normal aortic endothelium. In regenerating endothelium, there was a significant increase of the stress fiber to endothelial volume density ratio as compared to normal. Stress fibers were connected to cytoplasmic microfilament condensations located at the abluminal plasma membrane; the surface density of these condensations was significantly increased in regenerating endothelium as compared to normal. Filipin-cholesterol complexes were few or absent at stress fiber-membrane attachment sites but numerous in the remaining endothelial plasma membrane. This morphologic remodeling of the aortic endothelial cell layer may help to explain changes of endothelial cell function occurring in situations associated with increased cell turnover and motion.

Animals↗
PubMed2001

Dynamic reorientation of cultured cells and stress fibers under mechanical stress from periodic stretching.

Cell lines derived from rat aorta and frog kidney were cultured on elastic membrane, and mechanical stress was given to the cells by stretching the membrane periodically. Cell reorientation oblique to the direction of stretching occurred as a result of the rapid withdrawal of cell periphery located along the direction of stretching and gradual extension of the cell membrane toward the direction oblique to the direction of stretching. Dynamic reorganization of stress fibers in living cells was visualized by labeling stress fibers with TRITC(3)-actin or EGFP-tagged moesin fragments with actin-binding ability. Stress fibers aligned in the direction of stretching disappeared soon after the start of stretching and then obliquely reoriented stress fibers appeared. The stretch-induced reorientation of cultured cells was suppressed by an inhibitor of stretch-activated (SA) cation channels and by a Ca(2+) chelator. However, the rearrangement of stress fibers was not affected by these agents. From these results, we suggest that Ca(2+) influx via SA channels is involved in stretch-induced cell reorientation but stress fiber rearrangement is independent of SA channels. Therefore, cell reorientation does not simply depend on the arrangement of stress fibers but may be controlled by some additional mechanism(s) which is regulated by calcium signaling.

Actins↗
PubMed1999

A p85 subunit-independent p110alpha PI 3-kinase colocalizes with p70 S6 kinase on actin stress fibers and regulates thrombin-stimulated stress fiber formation in swiss 3T3 cells.

The signaling pathways linking receptor activation to actin stress fiber rearrangements during growth factor-induced cell shape change are still to be determined. Recently our laboratory demonstrated the involvement of p70 S6 kinase (p70(s6k)) activation in thrombin-induced stress fiber formation in Swiss 3T3 cells. The present work shows that thrombin-induced p70(s6k) activation is inhibited by the PI 3-kinase inhibitors wortmannin and LY-294002. These inhibitors also significantly reduced thrombin-induced stress fiber formation, demonstrating a role for PI 3-kinase activity in this process, most likely upstream of p70(s6k). Furthermore, the p110alpha form of PI 3-kinase was localized to actin stress fibers, as was previously shown for p70(s6k), as well as to a golgi-like distribution. In contrast, PI 3-kinase p110gamma colocalized with microtubules. The PI 3-kinase p85 subunit, known to be capable of association with p110alpha, was present in a predominantly golgi-like distribution with no presence on actin filaments, suggesting the existence of distinctly localized PI 3-kinase pools. Immunodepletion of p85 from cell lysates resulted in only partial depletion of p110alpha and p110alpha-associated PI 3-kinase activity, confirming the presence of a p85-free p110alpha pool located on the actin stress fibers. Our data, therefore, point to the importance of subcellular localization of PI 3-kinase in signal transduction and to a novel action of p85 subunit-independent PI 3-kinase p110alpha in the stimulation by thrombin of p70(s6k) activation and actin stress fiber formation.

3T3 Cells↗
PubMed2003

FHL3 is an actin-binding protein that regulates alpha-actinin-mediated actin bundling: FHL3 localizes to actin stress fibers and enhances cell spreading and stress fiber disassembly.

Four and a half LIM domain (FHL) proteins are members of the LIM protein superfamily. Several FHL proteins function as co-activators of CREM/CREB transcription factors and the androgen receptor. FHL3 is highly expressed in skeletal muscle, but its function is unknown. FHL3 localized to the nucleus in C2C12 myoblasts and, following integrin engagement, exited the nucleus and localized to actin stress fibers and focal adhesions. In mature skeletal muscle FHL3 was found at the Z-line. Actin was identified as a potential FHL3 binding partner in yeast two-hybrid screening of a skeletal muscle library. FHL3 complexed with actin both in vitro and in vivo as shown by glutathione S-transferase pull-down assays and co-immunoprecipitation of recombinant and endogenous proteins. FHL3 promoted cell spreading and when overexpressed in spread C2C12 cells disrupted actin stress fibers. Increased FHL3 expression was detected in highly motile cells migrating into an artificial wound, compared with non-motile cells. The molecular mechanism by which FHL3 induced actin stress fiber disassembly was demonstrated by low speed actin co-sedimentation assays and electron microscopy. FHL3 inhibited alpha-actinin-mediated actin bundling. These studies reveal FHL3 as a significant regulator of actin cytoskeletal dynamics in skeletal myoblasts.

Actinin↗
PubMed1998

Oblique alignment of stress fibers in cells reduces the mechanical stress in cyclically deforming fields.

The stress fiber (bundles of actin filaments) is one of the most prominent cytoskeletal components that contributes to the maintenance of cell architecture. It has generally been believed that upon cyclic stretching, both cells and their stress fibers become perpendicularly aligned to the direction of stretching. However, using our newly developed stretching device, we have recently found the contrary evidence that stress fibers in endothelial cells rapidly become rearranged at a specific oblique angle relative to the direction of stretching [Takemasa, T., K. Sugimoto, K. Yamashita: Exp. Cell Res. 230, 407-410 (1997)]. In light of this finding, we attempted to establish the explanation for such a phenomenon. First, we investigated the effects of possible modulators on the angle of the stress fibers; those were, modification of the stretching program, dependency of extracellular matrix types, and their reproducibility in other cell species. However, it seemed that the orientation was solely depending on the stretching amplitude applied. Next, we analyzed alterations in stress fiber length during loading tests using two kinds of deforming experiment systems. It was thus revealed that stress fibers aligned at a particular angle so as to minimize their length alterations in cyclic deforming fields. Rearrangement of the stress fibers at this angle probably occurs as a result of avoiding compressive stress and may be interpreted as a way of reducing the mechanical stress to which they are subjected during the deformation. This hypothesis well explains the reason not only for the survival of the stress fibers at a particular oblique angle, but also for the reduced numbers of stress fibers found at the other angles on cyclic deforming fields.

Actins↗
PubMed2005

Model of coupled transient changes of Rac, Rho, adhesions and stress fibers alignment in endothelial cells responding to shear stress.

Interactions of cell adhesions, Rho GTPases and actin in the endothelial cells' response to external forces are complex and not fully understood, but a qualitative understanding of the mechanosensory response begins to emerge. Here, we formulate a mathematical model of the coupled dynamics of cell adhesions, small GTPases Rac and Rho and actin stress fibers guiding a directional reorganization of the actin cytoskeleton. The model is based on the assumptions that the interconnected cytoskeleton transfers the shear force to the adhesion sites, which in turn transduce the force into a chemical signal that activates integrins at the basal surface of the cell. Subsequently, activated and ligated integrins signal and transiently de-activate Rho, causing the disassembly of actin stress fibers and inhibiting the maturation of focal complexes into focal contacts. Focal complexes and ligated integrins activate Rac, which in turn enhances focal complex assembly. When Rho activity recovers, stress fibers re-assemble and promote the maturation of focal complexes into focal contacts. Merging stress fibers self-align, while the elevated level of Rac activity at the downstream edge of the cell is translated into an alignment of the cells and the newly forming stress fibers in the flow direction. Numerical solutions of the model equations predict transient changes in Rac and Rho that compare well with published experimental results. We report quantitative data on early alignment of the stress fibers and its dependence on cell shape that agrees with the model.

Actin Cytoskeleton↗
PubMed2004

Assembly and reorientation of stress fibers drives morphological changes to endothelial cells exposed to shear stress.

Fluid shear stress greatly influences the biology of vascular endothelial cells and the pathogenesis of atherosclerosis. Endothelial cells undergo profound shape change and reorientation in response to physiological levels of fluid shear stress. These morphological changes influence cell function; however, the processes that produce them are poorly understood. We have examined how actin assembly is related to shear-induced endothelial cell shape change. To do so, we imposed physiological levels of shear stress on cultured endothelium for up to 96 hours and then permeabilized the cells and exposed them briefly to fluorescently labeled monomeric actin at various time points to assess actin assembly. Alternatively, monomeric actin was microinjected into cells to allow continuous monitoring of actin distribution. Actin assembly occurred primarily at the ends of stress fibers, which simultaneously reoriented to the shear axis, frequently fused with neighboring stress fibers, and ultimately drove the poles of the cells in the upstream and/or downstream directions. Actin polymerization occurred where stress fibers inserted into focal adhesion complexes, but usually only at one end of the stress fiber. Neither the upstream nor downstream focal adhesion complex was preferred. Changes in actin organization were accompanied by translocation and remodeling of cell-substrate adhesion complexes and transient formation of punctate cell-cell adherens junctions. These findings indicate that stress fiber assembly and realignment provide a novel mode by which cell morphology is altered by mechanical signals.

Actins↗
PubMed2000

Theoretical study of intracellular stress fiber orientation under cyclic deformation.

We studied stress fiber orientation under a wide range of uniaxial cyclic deformations. We devised and validated a hypothesis consisting of two parts, as follows: (1) a stress fiber aligns to avoid a mechanical stimulus in the fiber direction under cyclic deformation. This means that, among all allowable directions, a stress fiber aligns in the direction which minimizes the stimulus, i. e., the summation of the changes in length of the stress fiber over one stretch cycle; and (2) there is a limit in the sensitivity of the cellular response to the mechanical stimulus. Due to this sensing limit, the orientation angle in stress fibers is distributed around the angle corresponding to the minimum stimulus. To validate this hypothesis, we approximated an anisotropic deformation of the membrane on which cells were to be cultured. We then obtained the relationships between the stretch range and the fiber angle in the undeformed state which minimize the mechanical stimuli, assuming that the membrane on which stress fibers and cells adhered was homogeneous and incompressible. Numerical simulation results showed that the proposed hypothesis described our previous experimental results well and was consistent with the experimental results in the literature. The simulation results, taking account of the second part of the hypothesis with a small value for the limit in sensitivity to the mechanical stimulus, could explain why cell orientation is distributed so widely with cyclic stretch ranges of <10%. The proposed hypothesis can be applied to various types of deformation because the mechanical stimulus is always sensed and accumulates under cyclic deformation without the necessity of a reference state to measure the stimulus.

Animals↗
PubMed2004

Simultaneous stretching and contraction of stress fibers in vivo.

To study the dynamics of stress fiber components in cultured fibroblasts, we expressed alpha-actinin and the myosin II regulatory myosin light chain (MLC) as fusion proteins with green fluorescent protein. Myosin activation was stimulated by treatment with calyculin A, a serine/threonine phosphatase inhibitor that elevates MLC phosphorylation, or with LPA, another agent that ultimately stimulates phosphorylation of MLC via a RhoA-mediated pathway. The resulting contraction caused stress fiber shortening and allowed observation of changes in the spacing of stress fiber components. We have observed that stress fibers, unlike muscle myofibrils, do not contract uniformly along their lengths. Although peripheral regions shortened, more central regions stretched. We detected higher levels of MLC and phosphorylated MLC in the peripheral region of stress fibers. Fluorescence recovery after photobleaching revealed more rapid exchange of myosin and alpha-actinin in the middle of stress fibers, compared with the periphery. Surprisingly, the widths of the myosin and alpha-actinin bands in stress fibers also varied in different regions. In the periphery, the banding patterns for both proteins were shorter, whereas in central regions, where stretching occurred, the bands were wider.

Actinin↗
PubMed1999

Equations for estimating muscle fiber stress in the left ventricular wall.

Left ventricular muscle fiber stress is an important parameter in cardiac energetics. Hence, we developed equations for estimating regional fiber stresses in rotationally symmetric chambers, and equatorial and apical fiber stresses in prolate spheroidal chambers. The myocardium was modeled as a soft incompressible material embedding muscle fibers that support forces only in their longitudinal direction. A thin layer of muscle fibers then contributes with a pressure increment determined by the fiber stress and curvature. The fiber curvature depends on the orientation of the fibers, which varies continuously across the wall. However, by assuming rotational symmetry about the long axis of the ventricle and including a longitudinal force balance, we obtained equations where fiber stress is completely determined by the principal curvatures of the middle wall surface, wall thickness, and cavity pressure. The equations were validated against idealized prolate spheroidal chambers, whose wall thicknesses are such that the fiber stress is uniform from the equator to the apex. Because the apex is free to rotate, the resultant moment about the long axis of the LV must be zero. By using this constraint together with our fiber-stress equations, we were able to estimate a muscle fiber orientation distribution across the wall that was in qualitative agreement with published measurements.

Heart↗
PubMed1983

Differences in the stress fibers between fibroblasts and epithelial cells.

In the stress fibers of two types of nonmuscle cells, epithelia (PtK2, bovine lens) and fibroblasts (Gerbil fibroma, WI-38, primary human) the spacing between sites of alpha-actinin localization differs by a factor of about 1.6 as determined by indirect immunofluorescence and ultrastructural localization with peroxidase-labeled antibody. Both methods reveal striations along the stress fibers with a center-to-center spacing in the range of 0.9 mum in epithelial cells and 1.5 mum in fibroblasts. Periodic densities spaced at comparable distances are seen in PtK2 and in gerbil fibroma cells when they are treated with tannic acid and examined in the electron microscope. In such cells, densities are found not only along stress fibers but also at cell-cell junctions, attachment plaques, and foci from which stress fibers radiate. These latter three sites all stain with alpha-actinin antibody on the light and electron microscope level. Stress fibers in the two cell types also vary in the periodicity produced by indirect immunofluorescence with tropomyosin antibodies. As is the case for alpha-actinin, the tropomyosin center-to-center banding is approximately 1.6 times as long in gerbil fibroma cells (1.7 mum) as it is in PtK2 cells (1.0 mum). These results suggest that the densities seen in the electron microscope are sites of alpha-actinin localization and that the proteins in stress fibers have an arrangement similar to that in striated muscle. We propose a sarcomeric model of stress fiber structure based on light and electron microscopic findings.

Actinin↗
PubMed1992

The small GTP-binding protein rho regulates the assembly of focal adhesions and actin stress fibers in response to growth factors.

Actin stress fibers are one of the major cytoskeletal structures in fibroblasts and are linked to the plasma membrane at focal adhesions. rho, a ras-related GTP-binding protein, rapidly stimulated stress fiber and focal adhesion formation when microinjected into serum-starved Swiss 3T3 cells. Readdition of serum produced a similar response, detectable within 2 min. This activity was due to a lysophospholipid, most likely lysophosphatidic acid, bound to serum albumin. Other growth factors including PDGF induced actin reorganization initially to form membrane ruffles, and later, after 5 to 10 min, stress fibers. For all growth factors tested the stimulation of focal adhesion and stress fiber assembly was inhibited when endogenous rho function was blocked, whereas membrane ruffling was unaffected. These data imply that rho is essential specifically for the coordinated assembly of focal adhesions and stress fibers induced by growth factors.

3T3 Cells↗
PubMed1999

Syndecan-4 signals cooperatively with integrins in a Rho-dependent manner in the assembly of focal adhesions and actin stress fibers.

The assembly of focal adhesions and actin stress fibers by cells plated on fibronectin depends on adhesion-mediated signals involving both integrins and cell-surface heparan sulfate proteoglycans. These two cell-surface receptors interact with different domains of fibronectin. To attempt to identify the heparan sulfate proteoglycans involved, we used fibronectin-null (FN-/-) mouse fibroblasts to eliminate the contribution of endogenous fibronectin during the analysis. FN-/- fibroblasts plated on the cell-binding domain of fibronectin or on antibodies directed against mouse beta1 integrin chains attach but fail to spread and do not form focal adhesions or actin stress fibers. When such cells are treated with antibodies directed against the ectodomain of mouse syndecan-4, they spread fully and assemble focal adhesions and actin stress fibers indistinguishable from those seen in cells plated on intact fibronectin. These results identify syndecan-4 as a heparan sulfate proteoglycan involved in the assembly process. The antibody-stimulated assembly of focal adhesions and actin stress fibers in cells plated on the cell-binding domain of fibronectin can be blocked with C3 exotransferase, an inhibitor of the small GTP-binding protein Rho. Treatment of cells with lysophosphatidic acid, which activates Rho, results in full spreading and assembly of focal adhesions and actin stress fibers in fibroblasts plated on the cell-binding domain of fibronectin. We conclude that syndecan-4 and integrins can act cooperatively in generating signals for cell spreading and for the assembly of focal adhesions and actin stress fibers. We conclude further that these joint signals are regulated in a Rho-dependent manner.

Actin Cytoskeleton↗
PubMed1986

Probing the mechanism of incorporation of fluorescently labeled actin into stress fibers.

The mechanism of actin incorporation into and association with stress fibers of 3T3 and WI38 fibroblasts was examined by fluorescent analog cytochemistry, fluorescence recovery after photobleaching (FRAP), image analysis, and immunoelectron microscopy. Microinjected, fluorescein-labeled actin (AF-actin) became associated with stress fibers as early as 5 min post-injection. There was no detectable cellular polarity in the association of AF-actin with pre-existing stress fibers relative to perinuclear or peripheral regions. The rate of incorporation was quantified by image analysis of images generated with a two-dimensional photon counting microchannel plate camera. After equilibration of up to 2 h post-injection, FRAP demonstrated that actin subunits exchanged rapidly between filaments in stress fibers and the surrounding cytoplasm. When co-injected with rhodamine-labeled bovine serum albumin as a control, only actin was detected in the phase-dense stress fibers. The control protein was excluded from fibers and any linear fluorescence of the control was demonstrated as a pathlength artifact. The incorporation of AF-actin into stress fibers was studied by immunoelectron microscopy using anti-fluorescein as the primary antibody and goat anti-rabbit IgG coupled to peroxidase as the secondary antibody. At 5 min post-injection, reaction product was localized periodically in some fibers with a periodicity of approximately 0.75 microns. In large diameter fibers at 5 min post-injection, the analog was seen first on the surface of fibers, with individual filaments resolvable within the core. In the same cell, thinner diameter fibers were labeled uniformly throughout the diameter. By 20 min post-injection, most fibers were uniformly labeled. We conclude that the rate of actin subunit exchange in vivo is extremely rapid with molecular incorporation into actin filaments of stress fibers occurring as early as a few minutes post-injection. Exchange appears to first occur in filaments along the surface of stress fibers and then into more central regions in a periodic manner. We suggest that the periodic localization of actin at very early time points is due to a local microheterogeneity in which microdomains of fast vs. slower incorporation result from the periodic localization of actin-binding protein, such as alpha-actinin, along the length of the fiber.

Actin Cytoskeleton↗
PubMed2005

Cooperative effects of Rho and mechanical stretch on stress fiber organization.

The small GTPase Rho regulates the formation of actin stress fibers in adherent cells through activation of its effector proteins Rho-kinase and mDia. We found in bovine aortic endothelial cells that inhibitions of Rho, Rho-kinase, and mDia (with C3, Y27632, and F1F2Delta1, respectively) suppressed stress fiber formation, but fibers appeared after 10% cyclic uniaxial stretch (1-Hz frequency). In contrast to the predominately perpendicular alignment of stress fibers to the stretch direction in normal cells, the stress fibers in cells with Rho pathway inhibition became oriented parallel to the stretch direction. In cells with normal Rho activity, the extent of perpendicular orientation of stress fibers depended on the magnitude of stretch. Expressing active RhoV14 plasmid in these cells enhanced the stretch-induced stress fiber orientation by an extent equivalent to an additional approximately 3% stretch. This augmentation of the stretch-induced perpendicular orientation by RhoV14 was blocked by Y27632 and by F1F2Delta1. Thus, the activity of the Rho pathway plays a critical role in determining both the direction and extent of stretch-induced stress fiber orientation in bovine aortic endothelial cells. Our results demonstrate that the stretch-induced stress fiber orientation is a function of the interplay between Rho pathway activity and the magnitude of stretching.

Animals↗
PubMed1995

Focal adhesion proteins associated with apical stress fibers of human fibroblasts.

Human fibroblasts stained with fluorescently labeled phalloidin revealed many stress fibers within the apical cytoplasm in addition to those located along the basal plasma membrane and associated with focal adhesions. The staining patterns of these apical stress fibers with fluorescent phalloidin, anti-alpha-actinin, and antimyosin were identical to those of the basal stress fibers, suggesting the same macromolecular organization for both types of stress fibers. There were two types of apical stress fibers that clearly interacted with the apical plasma membrane, those extending between the basal and the apical plasma membrane and those having both ends on the basal membrane forming arches whose top interacted with the apical plasma membrane. By electron microscopy, we observed that apical stress fibers were associated with the apical plasma membrane via electron-dense plaques reminiscent of the focal adhesion. Since several proteins have been specifically localized to the focal adhesion site, we examined whether they were also present at the apical stress fiber-membrane association site by using immunocytochemical methods and image reconstruction techniques. We found that vinculin, talin, paxillin, a fibronectin receptor protein, several integrin subunits including beta 1, fibronectin, and proteins with phosphorylated tyrosine were also components of the apical plaque. These observations indicate that apical stress fibers are attached to the plasma membrane by using principally the same molecular assembly as the focal adhesion associated with the basal stress fiber. We suggest that the complex molecular organization of the focal adhesion is not demanded by cell adhesion, but rather it is needed for anchoring stress fibers to the plasma membrane. Apical plaques did not stain with the anti-integrin alpha v subunit or anti-focal adhesion associated kinase (FAK), although these antibodies stained focal adhesions. These results suggest that the apical stress fiber-membrane contact has some important functions different from those of the focal adhesion.

Antibody Specificity↗
PubMed1986

Expression and intracellular distribution of stress fibers in aortic endothelium.

Immunofluorescence microscopy was used to determine the number of endothelial cells with stress fibers for three age groups, and for three distinct anatomical locations within the descending thoracic aorta of both normotensive and spontaneously hypertensive rats. For each age group examined, hypertensive rats consistently demonstrated greater stress fiber expression than did normotensive rats. Neither age nor blood pressure was the predominant influence on stress fiber expression in aortic endothelium. In the normotensive rats, stress fiber expression remained unchanged for all age groups examined. For both strains, however, more endothelial cells with stress fibers were found in those regions where fluid shear stresses are expected to be high, when compared with those regions where the fluid shear stresses are expected to be low. This observation suggests that anatomical location, with its implied differences in fluid shear stress levels, is a major influence on stress fiber expression within this tissue. Electron microscopy was used to determine the intracellular distribution of stress fibers for both strains. Most stress fibers in both strains were located in the abluminal portion of the endothelial cells. This result is consistent with a role for stress fibers in cellular adhesion. However, the hypertensive rats had a higher proportion of stress fibers in the luminal portion of their cytoplasm than the normotensive rats. This increased presence of stress fibers in the luminal portion of the cell may be important in maintaining the structural integrity of the endothelial cell in the face of elevated hemodynamic forces in situ.

Actin Cytoskeleton↗